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Math Help - how many numbers less than or equal to N with all digits uniqueHi

  1. #1
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    how many numbers less than or equal to N with all digits uniqueHi

    Hi all

    I am really bad at combinatorics and need some help. I have stumbled on to the problem which states that

    "How many numbers upto N have all unique digits in them?"

    eg - suppose N = 34. Then answer is 31 (11, 22, 33 excluded, so 34 - 3 = 31). How do I solve this for a generic case? I cant understand how to extend the idea for 3 digits and above numbers.

    Any help would be appreciated. And please do explain your answer to. I would really be thankful for any help which can improve my combinatorics?

    Thanks
    Anant
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  2. #2
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    Re: how many numbers less than or equal to N with all digits uniqueHi

    problem posted here ...

    how many numbers less than or equal to N with all digits unique

    ... for the OP: please do not double post. The lobby is for introductions.
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